1. Field of the Invention
This invention relates to a single lens reflex camera, and more particularly, to a type of single lens reflex camera in which, while the light coming through an objective lens is reflected to a focusing screen by a main mirror that serves as a beam divider, the part of the light which passes through the main mirror is reflected out from the photo-taking light path by an auxiliary mirror which is positioned to operate independently of the main mirror, and in which the main and auxiliary mirrors are coordinated with each other and, further, there is provided an automatic diaphragm actuating lever for stopping down a diaphragm device in the objective lens mounting.
2. Description of the Prior Art
Many arrangements for focus detection in single lens reflex cameras have been proposed in which a portion of the light entering through an objective lens is directed to a light-sensitive element on which an image of the object is formed, and the output of the light-sensitive element representing a focusing condition at the film plane is utilized either in indicating the detection of a sharp focus, or as a control signal for automatic focus adjustment of the objective lens.
In single lens reflex cameras it is generally accepted from the optical standpoint, or on account of the assurance of coordination of the mirror mechanism, automatic diaphragm mechanism and shutter mechanism, that the light-sensitive element for focus detection or image sensor is arranged in the bottom panel of the mirror box. In order to direct to this light-sensitive element or image sensor a portion of the light coming through the objective lens, a main mirror is made half-mirrored in part or wholly, and an auxiliary mirror is provided behind the main mirror to reflect that portion of the light which passes through the main mirror to the light-sensitive element or image sensor.
Since such auxiliary mirror, when assuming a viewing position, lies in the path of light to the film, in order to make an exposure of the film, it must be moved away from the operative position along with the main mirror for finder. For this purpose, according to the prior art, the auxiliary mirror is hinged on the back of a main mirror support to be pivotable and operates in such a manner that when the main mirror is flipped upward, the auxiliary mirror also follows up and in the terminal position is in light-tight contact with the main mirror, as the mirror assembly is folded.
However, in a particular case where the focus detection is aimed for, as the degree of sharpness of an image formed by the objective lens on the film must be accurately reflected on the image-receiving surface of the light-sensitive element or image sensor, the requirement for precision of the positioning of the auxiliary mirror when in observing the object is so rigorous that such auxiliary mirror arrangement as described above is no longer put into actual practice. Therefore, it is seen here that this auxiliary mirror is arranged independently of the main mirror to facilitate the achievement of the required precision.
On the other hand, single lens reflex cameras are generally provided with an automatic diaphragm actuating member rendering it possible that, when the object is viewed, the diaphragm device in the objective lens mounting is set in the maximum possible aperture opening to perform the so-called light-metering at full open aperture, and when making an exposure of the film, prior to the opening of the shutter, the diaphragm device is stopped down to a required value of aperture. This automatic diaphragm actuating member is arranged to operate in response to a camera release and to complete its movement before the initiation of an exposure.
Therefore, as has been mentioned above, when the auxiliary mirror is provided independently of the main mirror, the result is that the camera has the three members independent of one another, namely, the main mirror, the auxiliary mirror and the automatic diaphragm actuating member. To these three independent members must be imparted respectively required motions by a drive mechanism when an exposure is to be made. In this case, since the above-described three members move independently of one another, said drive mechanism is liable to be complicated and have increased bulk and size. Particularly with the recently developed single lens reflex cameras, the tendency toward small size and compactness is so prominent that it is almost forbidden to use a new additional mechanism, or to increase the complexity and the bulk and size. Thus, in order to employ the mirror arrangement as described above, sufficient consideration must be taken regarding the design of the drive mechanism.